Xerographic apparatus with magnetic conveyor



Dec. 3, 1963 I R. H. HALL 3,113,042

XEROGRAPHIC APPARATUS WITH MAGNETIC CONVEYOR Filed April 19, 1960 2 Sheets-She'et 1 (I I 5 i FIG! 5 5 E 1 1 l l k I F: a

\w F/GZ 0 J l 15 1 F/G. 3 Mk I? 3/ INVENTORJR 30/ FIG 4 RICHARD HARRISON HALL A T TOR/VE Y Dec. 3, 1963 R. H. HALL 3,

XEROGRAPHIC APPARATUS WITH MAGNETIC CONVEYOR Filed April 19, 1960 2 Sheets-Sheet 2 A TTORNEY United States Patent 3,113,042 XEROGRAIHKC APPARATUS WlTH MAGNETIC CONVEYUR Richard Harrison Hall, Syracuse, N.Y., assignor to Xerox Corporation, a corporation of New York Filed Apr. 19, 1960, Ser. No. 23,274 7 Claims. (Cl. 1l$637) This invention relates to xerography and more particularly to development in xerography.

In the art of Xerography, an electrostatic latent image is formed on a suitable surface and made visible through the selective electrostatically-controlled deposition of particles on the latent image bearing surface. Various systems of development are known, but the ones most pertinent to the present invention are those commonly known as cascade development and magnetic brush development. In cascade development the developer material is a mixture of very fine particles calledtoner which are generally resinous in character and larger particles called carrier. The toner and carrier materials are so chosen that they acquire opposite electrical charges through triboelectrification whereby the toner particles stick to the carrier particles through electrostatic attraction. The triboelectric properties of the carrier particles are commonly achieved through the application of special surface coatings, and as a result, the body of the carrier particles may comprise diverse materials such as glass beads, carefully screened sand, iron filings, etc. When this developer mixture is cascaded across a latent image bearing surface the toner particles are selectively detached from the carrier particles and deposit on the surface in accordance with the latent image thereon, thus forming a visible image. Various modifications of cascade developer are known including the use of a liquid dielectric medium as one component as well as the use of developer materials having a single component or three or more components as well as the more common two components.

In magnetic brush development, a developer material is either a finely divided magnetic material or else comprises a cascade type material in which the carrier component is magnetically attractable. A magnet of some form is dipped into a reservoir of developer material and then withdrawn, thus forming on the poles of the magnet a brush-like structure resembling that commonly formed when a bar or horseshoe magnet is dipped in iron filings. This brush-like structure is then stroked across the latent image bearing surface causing selective deposition on the surface of particles from the brush. It is also possible to combine the two forms of development described above by cascading a magnetically attractable developer over an image bearing surface and employing magnetic fields adjacent to the surf-ace to modify the gravitationally induced flow pattern as described, for example, in Clark et al. US. Patent 2,880,696 issued on April 7, 1959.

The foregoing development systems are all characterized by the requirement for conveying quantities of a non-dispersed powder type material from some form of reservoir over an image bearing surface, back to a reservoir and repeating the process. In automatic machines this requirement has been met in the case of magnetic brush development with some form of traveling or rotating magnet structure and in the case of cascade development with a bucket conveyor or the like which lifts the developer from a reservoir, pours it over the image hearing surface, generally in the form of a Xerographic drum, from which it returns by gravity to the reservoir. These conveying methods are relatively cumbersome and complex. With certain Xerographic machine configurations the necessity for a developer conveyor greatly increases 3,1 lBfi iZ Patented Dec. 3, 1963 the size and complexity of the machine over that which it would have in the absence of a conveyor.

In accordance with the present invention it has been found that magnetic developer materials for cascade, magnetic brush or other forms of development may be conveyed by simple, novel and compact conveyor means.

It is accordingly an object of the present invention to provide novel xerographic developing methods and apparatus.

It is a further object to provide novel conveying methods and apparatus for powdered magnetic materials.

it is still a further object to provide novel methods and apparatus for con eying magnetic materials in which a magnetic field is made to move along a conveyor structure.

it is a further object to provide a stationary conveyor for magnetic materials.

These and other objects will become apparent from the following description and claims.

In the drawings:

FIG. 1 is a schematic representation of conveyor means according to the invention;

FIG. 2 is a schematic representation of a second form of conveyor;

FIG. 3 is -a schematic representation of a third form of conveyor;

FIG. 4 is a schematic representation of a fourth form of conveyor;

conveyor according to the invention;

FIG. 6 is a schematic cross-sectional view of one form of development apparatus according to the invention;

FIG. 7 is a modified form of apparatus according to FIG. 6;

FIG. 8 is a schematic View of a xerographic machine incorporating an embodiment of the invention; and

FIG. 9 is a schematic view of another form of Xerographic machine incorporating a different embodiment of the invention.

FIG. 1 shows a stationary magnetic conveyor accord ing to an embodiment of the, invention. It comprises generally conveyor 1 together with associated electrical apparatus. Conveyor 1 includes a number of magnetic armatures 19* which are positioned generally parallel to each other by a support block 11. These armatures may be of almost any shape, but are conveniently of a uniform rectangular cross-section as indicated in the drawing and may be as wide as the stream of developer to be conveyed. They may be constructed of any magnetically be made of virtually any structural material. Each armature it) is wound at its lower end with a coil 12. One end of each successive coil 12 is connected to a successive segment of commutator switch 13. The other ends of each coil are connected in common to battery 14 and thence to the rotor of commutator switch 13 which is driven by a slow speed motor 15. The lower ends of armatures dd are covered by a smooth cover plate 116 which may be made of any nonmagnetic material. As motor 15 turns commutator switch 13, each of coils 12 is energized in succession, thereby making a corresponding armature 10 an electromagnet which is capable of attracting a mass of magnetic developer material 17. Such a mass of developer is shown in the figure hanging beneath the armature which is shown as being energized. As the next successive armature is energized, the mass of magnetic material will slide over cover plate 16 until it is aligned with the next armature. This process keeps repeating so that, as long as the commutator switch is turning the mass of developer material will progress from armature to armature until it reaches one end or the other of the conveyor 1 at which point it will drop off. Although the developer is shown in the drawing as hanging beneath the conveyor structure, it is to be realized that the conveyor may be oriented in any position whatsoever and not merely in the downward facing position shown in the drawing. The commutator switch 13 should preferably be of the make-before-break type as indicated in the figure to assure that at least one armature is energized at all times. This prevents the developer material from falling off the conveyor during switching cycles, particularly where the conveyor is positioned carrying developer which faces downward as shown. Where the armatures have a sufficiently high magnetic remanence, the use of a make-before-break commutator is not necessary. The principal function of cover plate 16 is simply to provide a continuous smooth surface over which the developer may slide. It may be arbitrarily thin or may have a thickness of one-half inch or more. The use of a thicker cover plate permits the armatures to be spaced further apart, but since the developer is then positioned farther from the end of the armatures they must be magnetized more strongly to provide adequate attraction to the developer. In general, the operation of the conveyor is independent of the magnetic polarity of the individual armatures as a result of which may kinds of modifications can be made from the simple switching system shown in the figure.

FIG. 2 shows a modified form of the apparatus of FIG. 1. Here the lower ends of the armatures 10 are imbedded in a plastic block 20 or similar material which both positions the armatures and provides a smooth surface corresponding to that provided by cover plate 16 in FIG. 1. In accordance with the discussion given in connection with FIG. 1, the ends of the armatures may be flush with the surface of plastic block 20* as shown, or may extend beyond the ends of the armature, thereby keeping the attracted developer material at a distance from the armatures. This figure also shows a modification in the switching circuit whereby the rotor of commutator 13 has two arms instead of one, thereby simultaneously energizing two armatures instead of one. By this arrangement two separate masses of developer may be kept in motion across the conveyor. It is obvious that further arms may be added to the commutator providing only that the circuit is so arranged that at least sufficient space exists between energized armatures to maintain directional movement in the developer mass.

FIG. 3 shows still another form of conveyor according to the invention. In this embodiment the separate armatures of FIGS. 1 and 2 are replaced by a single magnetic member 30 having a series of teeth or pole pieces 31 along one face. Each such tooth or pole piece 31 is surrounded by a coil 12 which functions and is connected in exactly the same manner as the similarly numbered coils in FIGS. 1 and 2. The necessary smooth surface 16 upon which the developer must travel has been provided in this embodiment by filling in the spaces between pole pieces 31 with a hardenable casting resin.

FIG. 4 shows a further embodiment of the conveyor employing the same form of magnetic member as shown in FIG. 3. In this embodiment three sets of coils, 12a, 12b and 12c, are wound about pole pieces 31. Each coil is wound about two adjacent pole pieces and each group of coils 12a, 12b and 120 are spaced apart at intervals of three teeth. Each set of coils 12a, 12b and 12c is connected in common across a separate phase a, b, c of a three-phase electric power source 40 which is generally of less than power line frequency. In accordance with the generally known principles of polyphase electric motors, there is established on conveyor 1 a continuously moving set of alternating magnetic poles, although the conveyor structure itself is stationary. Non-magnetic cover plate 16 is included in order to provide a smooth surface over which the developer may slide iwhile following the moving magnetic poles. The use of coils which encircle more than one pole piece in this figure is illustrative only. Such coils may be used in the embodiment of FIG. 3 and, similarly, the single pole coils of FIG. 3 may be used in the embodiment of FIG. 4.

FIG. 5 is a perspective view of a conveyor 1 of the type shown in FIGS. 3 and 4. The electrical circuitry has been omitted for simplicity. This figure is included to illustrate the fact that the conveyors according to the present invention may be of arbitrary shape and may convey developer material along arbitrary, tortuous paths.

FIG. 6 shows a form of magnetic brush development apparatus according to the invention. It includes a fiat support member 60 over which is positioned a xerographic plate 61 which carries an electrostatic latent image on its upper surface. The formation of such a latent image may be carried out by various well-known techniques. A conveyor 1 is included, one end of which dips into a container 62 containing magnetic developer 17 and part of which passes closely adjacent to the latent image carrying surface of plate 61. The electrical circuitry, which is omitted for simplicity, may be of the type shown in any of the preceding figures and causes masses of developer to travel upward along the inner right side of the conveyor and to pass over the surface of the plate 61, rubbing against the surface of the plate as they do so. After passing over xerographic plate 61, the developer masses reach the end of conveyor 1 and drop back into container 62. In accordance with 'known xerographic principles, the latent image on plate 61 is developed through being contacted with developer 17. As should be apparent, modifications such as additional magnetic field control elements to draw the particles in closer contact with the surface to be developed or means to agitate the brush structure as it passes in contact with plate 61 may be incorporated herein and are within the scope of the invention.

The developer material used may be any of the types conventionally used in xerography for magnetic brush development. It will generally comprise a mixture of fine iron filings and micron size resinous powders. Although the resinous powder, which is the component deposited on the xerographic plate, is not in itself magnetic, it is carried along with the iron filings through electrostatic attraction.

In a further embodiment of this apparatus, FIG. 7, the xerographic plate itself may be adapted to or recessed within the operative side of the conveyor with the sensitive surface facing outward providing, of course, that the xerographic plate is not itself magnetic. In this further embodiment as in that shown in FIG. 6, the magnetic developer will be drawn across the surface of the xerographic plate by conveyor 1 and will effect development of the plate.

FIG. 8 is a schematic View of a rotating drum automatic cascade development xerographic machine and incorporating an embodiment of the present invention. Cascade development machines have hitherto employed as a developer a mixture of micron size resinous particles and much larger non-magnetic carrier beads. These beads must necessarily have special triboelectric properties which are most commonly obtained through the use of a special coating material. Since the triboelectric properties may be derived from the coating material, these beads can be made of magnetic material such as iron, iron oxide or ferrite particles without effecting the xerographic properties of the developer mixture. Such a magnetic mixture is accordingly used in this machine which includes a rotating xerographic drum 70, charging apparatus 71, a lens 72, microfilm roll 73 and lamp 74 which cooperate to project an image on drum 70, a transfer roller 75 and paper 76 and a cleaning brush 77. These elements are all conventional and operate in their conventional and well-known manner. Accordingly, they are only shown schematically in the figure and their functioning will not be further described. The development portion of this machine comprises a container 62. filled with a developer material 17 and positioned beneath and to one side of xerographic drum 70. A conveyor 1 of the form shown in FIG. 2 is positioned to lift the developer material out of container 62 and release it over the top of the drum at a point somewhat to the right thereof. The developer then cascades over the surface of the drum developing it in the known manner and returns to container 62. Although the developer will generally include a non-magnetic resinous component, it has already been pointed out that this component is electrostatically adherent upon the magnetic particles and therefore is conveyed together with those particles. A shield '78 is included as a part of the conveyor to prevent developer material from being carried up the back or rear part of the conveyor. The electrical circuitry is not shown, but may be that of any of FIGS. 1 through 4 or their equivalents. It is readily apparent that the stationary conveyor of the present invention is a much simpler and more compact structure than an equivalent bucket type conveyor for the same purpose. In addition to having no moving parts, the conveyor of the present invention may readily be formed in a curved shape and requires no return flight.

FIG. 9 is a schematic view of a different form of xerographic machine embodying the present invention. The xerographic portion of this machine is the same as that of FIG. 8 except that the developer material is fed to the clockwise rotating xerographic drum at a point to the left of the top thereof. A curved chute 80 is provided to direct the developer against the surface of the drum at relatively high speed and in the direction of rotation of the drum. The inertia of the fast moving developer causes it to travel over the top of the drum and cascade down the right side of the drum rather than falling down the left side. This form of development is known as over-the-top development and has many advantages for high speed Xerographic machines which are more fully set forth in the simultaneously filed application Serial No. 22,439 in the name of Lehmann et al., and entitled Cascade Development Improvement. This type of machine is particularly inconvenient to construct with a conventional mechanical developer conveyor because the conveyor would have to be very long in order to provide adequate clearance from the xerographic'drum 70 and yet carry the developer to the far side of the drum. These requirements are readily met, however, by using a curved developer and a curved conveyor in accordance with the present invention. In this xerographic machine configuration it is generally more convenient to carry the developer up the outside surface of the curved conveyor as illustrated in this figure rather than up the inside surface as illustrated in FIG. 8. This has the further advantage of positioning the magnetic influence at a greater distance from the surface being developed than if the particles were moved upward between the drum and the conveyor which prevents the magnetic members from effecting the cascading particles developing the drum.

The present invention has been described and illustrated in terms of certain illustrative embodiments and in terms of certain illustrative applications only. It is obvious that, in accordance with the principles set forth, the conveyors of the invention can be constructed in many different forms which would be immediately obvious to one skilled in the art, and these various forms are intendedto be encompassed within the appended claims. Similarly, the utility of the invention is not confined to the illustrations contained herein, but is adaptable to a wide variety of xerographic and other applications.

What is claimed is:

1. A xerographic apparatus comprising a reservoir of magnetically attractable xerographic developing material,

a stationary, smooth surfaced, non-magnetic, elongated member having a first end extending into said reservoir, a xerographic plate embedded in a portion of said non-magnetic member remote from said reservoir, said xerographic plate having its photoconductive insulating surface flush with the smooth surface of said non-magnetic member, an array of stationary electromagnets behind the smooth surface of said non-magnetic member and extending at least from said reservoir to the end of said xerographic plate which is most remote from said reservoir and means to sequentially energize said electromagnets whereby said developing material is caused to move smoothly and continuously from said reservoir across and in very close proximity to the photoconductive insulating surface of said xerographic plate so as to develop it.

2. Xerographic apparatus according to claim 1 in which said reservoir extends below and beyond the terminal point of the magnetically controlled feed path of said developing material whereby said developing material is returned to said reservoir by gravity feed after it has passed over said xerographic plate.

3. Apparatus according to claim 1 in which the electromagnet energizing means comprises at least one DC. power source which is sequentially connected to each successive electromagnet coil through a rotating commutator switch.

4. A xerographic apparatus comprising a reservoir of magnetically attractable xerographic developing material, a stationary, smooth surfaced, non-magnetic, elongated member having a first end extending into said reservoir, a xerogr-aphic plate with its photoconductive insulating surface spaced slightly from and facing a portion of said non-magnetic member remote from said reservoir, an array of stationary electromagnets behind the smooth surface of said non-magnetic member and extending at least from said reservoir to the end of said Xerographic plate which is most remote from said reservoir, and means to sequentially energize said electromagnets whereby said developing material is caused to move smoothly and continuously from said reservoir across the photoconductive insulating surface of said xerographic plate so as to develop it.

5. Xerographic apparatus according to claim 4 in which said reservoir extends below and beyond the terminal point of the magnetically controlled feed path of said developing material whereby said developing material is returned to said reservoir by gravity feed after it has passed over said xerographic plate.

6. Xerographi-c apparatus for developing a cylindrical, electrostatic latent image bearing member rotating about a'substantially horizontal axis in a first direction comprising a steeply inclined chute with a smooth bend near its bottom positioned to discharge granular, magnetically attractable, electroscopic developing material against said cylindrical image bearing member along a line which is substantially tangential to the periphery of said image bearing member, in the same direction as the direction of rotation of said image bearing member and at a point prior to the uppermost point in its rotation, said chute being sufficiently long and steep to accelerate said granular electroscopic material to a velocity sufficient to cause said developing material to travel at a speed greater than that of the peripheral speed of the rotating member and a sufficient velocity to move over the top of said cylindrical image bearing member, a reservoir positioned toward the bottom of said cylindrical image bearing member to collect the granular electroscopic developing material which falls from the surface of said cylindrical latent electrostatic image bearing member after its travel across the surface of said image bearing member, a stationary, smooth surfaced, non-magnetic, elongated member having a first end in said reservoir and extending up and over said cylindrical latent electrostatic image bearing member in spaced relation therewith, and terminating at the top of said inclined chute, an array of stationary electromagnets behind the smooth surface of said non-magnetic member extending for substantially its complete length and means to sequentially energize said electromagnets whereby granular electroscopic developing material presented to said cylindrical image bearing member by said inclined chute is recycled to the top of said inclined chute after it has passed over the surface of said cylindrical image bearing member and into said reservoir.

7. A xerographic apparatus comprising a reservoir of magnetically attractable xerographic developing material, a latent electrostatic image bearing member, means to cause said developing material to move through a cycle from said reservoir to a point on the surface of said latent electrostatic image bearing member along at least a portion of the surface of said latent electrostatic image bearing member and then back to said reservoir, said means for causing said developing material to move through said cycle including a smooth surfaced stationary non-magnetic elongated member having a first end extending into said reservoir, an array of stationary electromagnets behind the smooth surface of said non-magnetic member extending for substantially its complete length and means to sequentially energize said electromagnets whereby said developing material is caused to move smoothly and continuously from said reservoir through at least a portion of said cycle.

References Cited in the file of this patent UNITED STATES PATENTS 619,636 Trustedt Feb. 14, 1-899 790,342 Campbell May 23, 1905 871,301 Schwarz Nov. 19, 1907 1,020,943 Bachelet Mar. 19, 1912 1,425,235 Bradley Aug. 8, 1922 2,832,311 Byrne Apr. 29, 1958 2,880,696 Clark et al Apr. 7, 1959 

7. A XEROGRAPHIC APPARATUS COMPRISING A RESERVOIR OF MAGNETICALLY ATTRACTABLE XEROGRAPHIC DEVELOPING MATERIAL, A LATENT ELECTROSTATIC IMAGE BEARING MEMEBER, MEANS TO CAUSE SAID DEVELOPING MATERIAL TO MOVE THROUGH A CYCLE FROM SAID RESERVOIR TO A POINT ON THE SURFACE OF SAID LATENT ELECTROSTATIC IMAGE BEARING MEMEBER ALONG AT LEAST A PORTION OF THE SURFACE OF SAID LATENT ELECTROSTATIC IMAGE BEARING MEMBER AND THEN BACK TO SAID RESERVOIR, SAID MEANS FOR CAUSING SAID DEVELOPING MATERIAL TO MOVE THROUGH SAID CYCLE INCLUDING A SMOOTH SURFACED STATIONARY NON-MAGNETIC ELONGATED MEMBER HAVING A FIRST END EXTENDING INTO SAID RESERVOIR, AN ARRAY OF STATIONARY ELECTROMAGNETS BEHIND THE SMOOTH SURFACE OF SAID NON-MAGNETIC MEMBER EXTENDING FOR SUBSTANTIALLY ITS COMPLETE LENGTH AND MEANS TO SEQUENTIALLY ENERGIZE SAID ELECTROMAGNETS WHEREBY SAID DEVELOPING MATERIAL IS CAUSED TO MOVE SMOOTHLY AND CONTINUOUSLY FROM SAID RESERVOIR THROUGH AT LEAST A PORTION OF SAID CYCLE. 